Fantastic Voyage - By Isaac Asimov Page 0,41

Proteus.

They could hear it-like the distant boom of artillery. It was only a rhythmic vibration of the floor of the ship, slow and measured, but growing louder. A dull thud, followed by a duller; a pause, then a repetition, louder, always louder.

"The heart!" said Cora. "It is."

"That's right," said Michaels, "slowed a great deal."

"And we don't hear it accurately," said Duval, with dissatisfaction. The sound waves are too immense in themselves to affect our ear. They set up secondary vibrations in the ship but that's not the same thing. In a proper exploration of the body ..."

"At some future time, doctor," said Michaels. "It sounds like cannon," said Grant.

"Yes, but it lays down quite a barrage; two billion heartbeats in threescore years and ten," said Michaels. "More."

"And every beat," added Duval, "is the thin barrier separating us from Eternity, each giving us time to make our peace with ..."

"These particular beats," said Michaels, "will send us straight to Eternity and give us no time at all. Shut up, all of you. Are you ready, Owens?"

"I am. At least I'm at the controls and I've got the chart before me. But how do I find my way through this?"

"We can't get lost, even if we try. We're in the superior vena cava now, at the point of junction with the inferior. Got it?"

'Yes

"All right. In seconds, we'll be entering the right atrium, the first chamber of the heart-and they had better stop the heart, too. Grant, radio our position."

Grant was momentarily lost to all else in his fascination with the view ahead. The vena cava was the largest vein in the body, receiving in the final stretch of its tube all the blood from all the body but the lungs. And as it gave way to the atrium, it became a vast resounding chamber, the walls of which were lost to sight so that the Proteus seemed to ho within a dark, measureless ocean. The heart was a slow, terrifying pound now, and at each steady thud, the ship seemed to lift and tremble.

At Michaels' second call, Grant snapped back to life and turned to his radio transmitter.

Owens called out, "Tricuspid valve ahead."

The others looked ahead. At the end of a long, long corridor, they could see it in the far distance. Three sparkling red 'sheets, separating and billowing open as they moved away from the ship. An aperture yawned and grew larger while the cusps of the valve fluttered each to its respective side.. There beyond it was the right ventricle, one of the two main chambers.

The' blood-stream moved into the cavity as though being pulled by a powerful suction. The Proteus moved with it so that the aperture approached and enlarged at a tremendous rate. The current was smooth, however, and the ship rode it with scarcely a tremor.

Then came the sound of the thunderous boom of the ventricles, the main, muscular chambers of the heart, as they contracted in systole. The leaves of the tricuspid valve ballooned back toward the ship, moving slowly shut, with a wet, smacking contact that closed the wall ahead into a long vertical furrow that parted into two above.

It was the right ventricle that lay on the other side of the now-closed valve. As that ventricle contracted, the blood could not regurgitate through the atrium and was forced instead into and through the pulmonary artery.

Grant called out above the reverberating boom. "One more heartbeat and that will be the last, they say."

Michaels said, "It had better be, or it's our last heartbeat, too. Shove on through, full speed, Owens, the instant the valve opens again."

There was firm determination in his face now, Grant noted absently-no fear at all.

The radioactive sensors that had hovered about Benes' head and neck were now clustered over his chest, over a region from which the thermal blanket had been folded hack,

The charts of the circulating system on the wall had expanded now in the region of the heart and showed only part of the heart-the right atrium. The blip that marked the position of the Proteus had moved smoothly down the -vena cava into the lightly muscled atrium which had expanded as they entered, then contracted.

The ship had, in one bound, been pushed nearly the length of the atrium toward the tricuspid valve, which closed just as they were at its brink. On an oscilloscopic scanner, each heartbeat was being translated into a wavering electronic beam and it was watched narrowly.

The electro-shock apparatus was in position; and the